Zirconium alloy treatment process



United States Patent 3,121,034 ZIRCGNIUM ALLOY 'IREATEMENT PRGCESS KurtAnderlto, Frankfurt am Main, and Herbert Richter,

Frankfurt am Main, Niederrad, Germany, and Hans- Walter Schleicher,Chivasso, Italy, assignors to the United States of America asrepresented by the United States Atomic Energy Commission No Drawing.Filed Mar. 13, 1962, Ser. N 175 ,45 4 4 Claims. (Cl. 148-115) Thisinvention relates to a novel process of making nuclear reactorcomponents and more particularly to a process of increasing thecorrosion resistance of nuclear reactor components that are made fromzirconium base alloys that contain from 0.5% to 5% by weight of niobiumand which may optionally contain up to 3% by Weight of tin and which mayalso optionally contain in addition to tin up to 2% by Weight of one ofthe metals: iron, nickel, chromium, tantalum, palladium, molybdenum, andtungsten.

Binary zirconium base alloys containing from 0.5% to 5% by weight ofniobium have been used as components of nuclear reactors and moreparticularly as cladding for fuel elements that are subject to corrosionby pressurized water or steam. Such alloys are generally soft annealedat temperatures above 640 C., e.g. at 900 C., after a hot formingoperation, but the metal structure thus obtained displays anunsatisfactory resistance to corrosion by hot pressurized water orsteam. The corrosion resistance of these alloys is somewhat improved ifthe annealing operation at 900 C. is followed by quenching and then thealloys are further annealed at a temperature of 500 to 600 C. However,these additional steps still fail to give these alloys the desireddegree of resistance to corrosion.

This invention has as an object the preparation of nuclear reactorcomponents that are resistant to corrosion by steam or hot water andthat are made from zirconium base alloys containing niobium. A furtherobject of this invention is to provide a simple technique for increasingthe corrosion resistance of reactor components made from zirconium basealloys containing niobium. Other objects will be apparent from thefollowing description of the invention.

These objects are accomplished by the present invention which relates tothe annealing at a temperature between 550 C. and 600 C. of articlesmade by cold shaping zirconium base alloys containing niobiumimmediately after said articles have been cold shaped. The zirconiumbase alloys to which the present invention pertains include binaryzirconium-niobium alloys containing from 0.5 to 5% by weight of niobium,ternary zirconium-niobium-tin alloys containing from 0.5 to 5% by weightof niobium and up to 3% by weight of tin, and quaternary zirconium basealloys containing from 0.5 to 5% by weight of niobium, up to 3% byweight of tin, and up to 2% by weight of a fourth metal selected from te "roup consisting of iron, nickel, chromium, tantalum, palladium,molybdenum, and tungsten.

In order to improve the corrosion resistance of reactor components to bemade from the zirconium base alloys hereinabove indicated, they arefirst cold shaped and subsequently subjected to a heat treatment between3,i2l,034 Patented Feb. 11, 1964 ice 2 550 C. and 600 C. The term coldshaping is used to denote a shaping of the component within atemperature range in which no recrystallization of the structure takesplace. Such cold shaping may therefore be performed at temperatures upto about 550 C. For practical reasons, the shaping is usually carriedout at ambient temperatures. Prior to the cold shaping the component mayhave been soft annealed at temperatures between 640 C. and 1000 C. As analternative procedure, the component may have been hot shaped attemperatures between 640 C. and 1000 C., and then either quenched orslowly cooled in air before being subjected to the cold shaping step ofthe present invention.

The duration of the annealing treatment applied in accordance with thepresent invention is determined by the temperature of annealing and alsoby the extent of reduction of the component. An article formed from azirconium base alloy containing 1% by weight of niobium and reduced by60% by cold shaping shows a considerable improvement in its corrosionresistance after a heat treatment at 575 C. for 60 minutes. If theannealing temperature is increased, the duration of the annealingtreatment may be reduced. The duration of the annealing operation is notlimited. However, the annealing operation is usually terminated when thedesired improvement of the articles corrosion resistance has beenachieved.

After annealing in accordance with the invention, the component iscooled or quenched as desired.

The heat treatments of the components at 550600 C. in accordance withthe present invention are in the nature of final annealing treatments.No further annealing can be carried out which will nullify theimprovement in corrosion resistance that has been attained. Therefore,while no harm will result from a short annealing treatment below 500 C.,no annealing at temperatures in excess of 600 C. can be tolerated.

The heat treatments of the present invention are in all cases appliedsubsequent to cold shaping operations. However, several cold shapingoperations may precede the heat treatment. Between these prior coldshaping operations the articles may be annealed at temperatures between640 C. and 1000 C. in accordance with prior art practice. After a heattreatment in accordance with the present invention, a further coldshaping operation may be performed. However, such a shaping operationshould be a minor one, involving a reduction of less than 20%. The heattreatments made in accordance with the present invention may also beapplied as intermediate treatments between several cold shapings.

The process of the present invention imparts a pronounced improvement inthe corrosion resistance of the zirconium base alloys thus treated asmay be seen from the following examples.

EXAMPLE 1 Corrosion tests were carried out on sheets 1.8 mm. thick madefrom binary zirconium-niobium alloys containing 1% and 3% by weight ofniobium. In one group of these tests the sheets were exposed to steam at400 C. at a pressure of 200 atmospheres (2,845 pounds per square inch)for a period of 1500 hours. In another group of these tests the sheetswere submerged in pressurized water at 350 C. at saturation pressure for1500 hours. The results of these tests are indicated below in Table 1.The data in line A of this table pertains to sheets that had beenannealed at 900 C. for 2 hours and then quenched in water in accordancewith a known prior art technique. The data in line B of this tablepertains to sheets that had been annealed at 900 C. for 2 hours,quenched in water, reannealed at 575 C. for 48 hours and then cooled inair in accordance with known prior art practice. The data in line C ofthis table pertains to sheets that had been cold shaped to a 60%reduction and then annealed for 48 hours at 575 C. followed by aircooling in accordance with the present invention. Comparison of the datain line C with the data given on lines A and B shows the clearsuperiority of the present invention over prior art practices.

Table 1 [Increase in weight (mg. per dm.'

Steam at 400 0. Water at 350 0.

Line

Zr1% Zr-3% Zr1% Zr3% Nb Nb Nb Nb A 120 200 49 72 B 88 78 40 35 C 61 6431 20 EXAMPLE 2 Test samples of a ternary zirconium base alloycontaining 0.5% by Weight of niobium and 1% by weight of tin wereexposed to steam at 400 C. at a pressure of 200 atmospheres for a periodof 1900 hours. One sample which was merely annealed for 24 hours at 700C. showed an increase in weight of 123 mg. per dm. after testing. Theother sample was not only annealed for 24 hours at 700 C., but also coldshaped to 50% reduction at ambient temperature and then heat treated for24 hours at 590 C. in accordance with the present invention. This lattersample showed only an increase in weight of 107 mg. per dm. aftertesting.

EXAMPLE 3 Test samples of a ternary zirconium base alloy containing 2%by weight of niobium and 1% by weight of tin were exposed to steam at400 C. at a pressure of 200 atmospheres for a period of 1900 hours. Onesample that Was merely annealed for 24 hours at 700 C. showed anincrease in weight of 195 mg. per dm. after testing. The other samplewas not only annealed for 24 hours at 700 C., but also cold shaped to50% reduction at ambient temperature and then heat treated for '24 hoursat 590 C. in accordance with the present invention. This latter sampleshowed only an increase in weight of 120 mg. per dm. after testing.

EXAMPLE 4 The following table gives the results of 500 hours of exposureto steam at 400 C. and at 480 C. of three quaternary zirconium basealloys containing niobium, tin

invention.

Table 2 Increase in Weight Composition of Zirconium Base Steam (mg. perdm?) Alloy Temperature, C.

Zr-2% Nb0.5% Sn-0.3% Cr 400 74 32 Zl2% Nb0.5% SI10.3% Or 480 270 220Zr2% Nb0.5% S110.3% M0 400 116 84 Zr-2% bib-0.5% S1'10.3% M0 480 305 245Zr-5% Nb1% Sn0.2% Pd 400 62 EXAMPLE 5 The quaternary zirconium basealloy containing 5% by weight of niobium, 1% by weight of tin, and 0.2%by weight of palladium was also submerged in pressurized water at 350 C.for 500 hours. The sample thereof that had been merely heat treated for1 hour at 650 C. and then air cooled gained 77 mg. per dm. but thesample thereof that had been reduced 50% by cold shaping followed bysubsequent heat treatment at 575 C. for 240 hours in accordance with thepresent invention and then cooled in air gained only 47 mg. per dm. Thisexample further illustrates the advantage of the present invention.

Resort may be had to such modifications and variations as fall withinthe teachings of the above specification and the scope of the appendedclaims.

We claim:

1. A process of preparing zirconium base alloys of improved corrosionresistance for use in a nuclear reactor comprising making 50 to 60percent reductions by cold shaping the zirconium base alloys selectedfrom the group consisting of binary zirconium-niobium alloys containingfrom 0.5 to 5% by weight of niobium, ternary zirconiumniobium-tin alloyscontaining from 0.5 to 5% by weight of niobium and up to 3 by weight oftin, and quaternary Zirconium base alloys containing from 0.5 to 5% byweight of niobium, up to 3% by weight of tin, and up to 2% by weight ofa fourth metal selected from the group consisting of iron, nickel,chromium, tantalum, palladium, molybdenum, and tungsten, at atemperature not above 550 followed by an annealing of said cold shapedalloy at a temperature between 550 C. and 600 C. for a period of from 1to 240 hours and subsequently air cooling whereby improved steam and hotWater corrosion resistance is effected.

2. A process as recited in claim 1 in which the cold shaping isperformed at ambient temperatures.

3. A process according to claim 1 in which the zirconium base alloys arehot shaped at 640 C. to 1000 C. and air cooled prior to cold shaping.

4. A process according to claim 1 in which the zirconium base alloys aresoft annealed at 640 C. to 1000 C. and air cooled prior to cold shaping.

References Cited in the file of this patent UNITED STATES PATENTS US.Dept. of Interior, March 1950, pages 19 and 20 relied on.

Development of Zirconium Base Alloys, G. E. Re-

.search Laboratory, Jan. 1, 1950, page 3 relied on.

1. A PROCESS OF PREPARING ZIRCONIUM BASE ALLOYS OF IMPROVED CORROSIONRESISTANCE FOR USE IN A NUCLEAR REACTOR COMPRISING MAKING 50 TO 60PERCENT REDUCTIONS BY COLD SHAPING THE ZIRCONIUM BASE ALLOYS SELECTEDFROM THE GROUP CONSISTING OF BINARY ZIRCONIUM-NIOBIUM ALLOYS CONTAININGFROM 0.5 TO 5% BY WEIGHT OF NIOBIUM, TERNARY ZIRCONIUMNIOBIUM-TIN ALLOYSCONTAINING FROM 0.5 TO 5% BY WEIGHT OF NIOBIUM AND UP TO 3% BY WEIGHT OFTIN, AND QUATERNARY ZIRCONIUM BASE ALLOYS CONTAINING FROM 0.5 TO 5% BYWEIGHT OF NIOBIUM, UP TO 3% BY WEIGHT OF TIN, AND UP TO 2% BY WEIGHT OFA FOURTH METAL SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL,CHROMIUM, TANTALUM, PALLADIUM, MOLYBDENUM, AND TUNGSTEN, AT ATEMPERATURE NOT ABOVE 550* FOLLOWED BY AN ANNEALING OF SAID COLD SHAPEDALLOY AT A TEMPERATURE BETWEEN 550*C. AND 600* C. FOR A PERIOD OF FROM 1TO 240 HOURS AND SUBSEQUENTLY AIR COOLING WHEREBY IMPROVED STEAM AND HOTWATER CORROSION RESISTANCE IS EFFECTED.